Various methods and apparatus have heretofore been used for joining layers of heat sealable plastic or thermal plastic layers, which generally utilize a heated sealing bar or electrode which is brought into engagement with the plastic layer. The heated sealable bar melts the plastic and the pressure of the bar against the plastic forms a thermal weld.
For example, U.S. Pat. No. 2,947,345 discloses a single straight hot knife blade that overlies a cutting and sealing roll normally in spaced relation and is adapted to be depressed there against when the thermal plastic webs have advanced to their proper positions on the cutting and sealing roll so as to seal and cut said thermal plastic webs.
Furthermore, U.S. Pat. No. 3,706,177 teaches a sealing unit mounted on a framework which permits up and down movement thereof so as to accommodate bags of slightly varying heights.
Moreover, U.S. Pat. No. 4,455,134 illustrates a hand operated thermal press for installing metal inserts in a workpiece of thermal plastic material.
Finally, U.S. Pat. No. 2,154,521 discloses the clamping of heat forming tools for sealing filled containers.
Each of such prior art heat sealing structures including those referred to above generally utilize a bar, electrode or roller which is adapted to be pressed against another bar, electrode or roller so as to seal thermal plastic materials therebetween.
Over a prolonged period of usage, such heat sealable bars, electrodes or rollers become worn and exhibit localized wear spots in those areas of repeated application of heat and pressure which results in less efficient thermal bonding of plastic film.
Furthermore, in those arrangements where a heat sealable bar configured in the shape of a knife is repeatedly reciprocally pressed against another bar, such knife edge relatively quickly imparts a "wear groove" localized within the area of contact with the other bar.
Moreover in those arrangements where a heat sealable bar contacts a roller such rollers become unevenly worn and tend to lose their roundness and thereafter experience erratic rotational patterns.
It is an object of this invention to provide for a more efficient heat sealable bar.
It is a further object of this invention to provide heat sealable bars which substantially eliminate localized wear characteristics over prolonged usage.